Jenny asked. Hi Everyone, I was hoping to get some words of wisdom on my oscillator that only oscillates in simulation! I have a MEMS device that resonates around 34 MHz at a given bias with Q of 100.
You have already received some very good advice. You might also try a transistor with a higher ft. My personal experience is that it's easier to get an FET to oscillate in a colpits configuration. You won't be able to drive a 50 ohm load from an FET. A buffer of some kind will definitely be needed. Regards. Max. K 4 O D S. Email: [EMAIL PROTECTED] Transistor site http://www.funwithtransistors.net Vacuum tube site: http://www.funwithtubes.net Music site: http://www.maxsmusicplace.com To subscribe to the fun with tubes group send an email to, [EMAIL PROTECTED] ----- Original Message ----- From: "Jenny Lee" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Monday, March 31, 2008 4:20 PM Subject: [time-nuts] Xtal-like Colpitts Oscillator Hi Everyone, I was hoping to get some words of wisdom on my oscillator that only oscillates in simulation! I have a MEMS device that resonates around 34 MHz at a given bias with Q of 100. I fit the impedance into a six-element equivalent model (similar to 4-element equivalent model of Quartz) and placed in a Colpitts configuration for the simulation. In the open-loop gain/phase plot, the peak barely passes 0 dB no matter what C1 and C2 I chose. For transient simulation, it does oscillates, but on a PCB, the circuit won't oscillate! I'm including the device impedance, circuit schematics and simulation results as an attachment. I've managed to oscillate 20 MHz device which has a higher maximum impedance than 34 MHz devices both in simulation and on a PCB - but for this I followed the guidelines of Colpitts for Quartz ranging at 10~20MHz. But above 20 MHz, for Quartz, overtones seem to be the way to go due to the manufacturing so I couldn't find any reference or circuits that operates Quartz for 30 MHz~50MHz ranges at a fundamental mode. I can only use fundamental mode for my device... I would really appreciate if you could share some of your experiences with Colpitts or any suggestions of what I can try to make it work... Thank you!-Jenny _________________________________________________________________ In a rush? Get real-time answers with Windows Live Messenger. http://www.windowslive.com/messenger/overview.html?ocid=TXT_TAGLM_WL_Refresh_realtime_042008 -------------------------------------------------------------------------------- > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
